1. Field of the Invention
This invention relates to a method and apparatus that will allow an engine to operate closed-loop in a desired air/fuel controlled--enleanment condition following a cold or warm start, highway cruise or other general dynamic operational condition. The method and system of the present invention will optimize air/fuel control for each individual vehicle or engine.
2. Description of the Prior Art
The operation of an internal combustion engine in an enleaned condition has been significantly elusive because a true feedback system is required to anticipate any conditions other than those for which an engine was originally configured and calibrated for. True feedback systems have been less than satisfactory because they generally rely on heated exhaust gas oxygen sensors (HEGO) or heated universal exhaust gas oxygen sensors (UEGO), which take a significant period of time to become operational and which are subject to damage or chemical poisons which cause improper signal outputs. These sensors have other problems such as a propensity to have a sluggish response when the sensors are subjected to a large mass of chemical reactants or when cold. These sensors also have a limited life span and are not useful in some applications.
An internal combustion engine, when started cold or even hot, does not have perfect fuel utilization. An excess of fuel is generally introduced into the intake system to insure that a good igniting and burning of the air/fuel mixture is maintained. The excessive fuel introduced into the system is almost impossible to quantify and control due to a number of reasons such as actual fuel composition, such as RVP (Reeds Vapor Pressure), and variable engine operational condition(s). Engine intake deposits, which change over time, also play a significant role in the proper fueling of said engines. Generally most of the regulated emissions emitted into the atmosphere by vehicles are produced during this period of engine operation, that is, during the first 30 to 90 seconds after cold (or warm) engine start. This is the period that the engine usually operates "open-loop". This means that a closed-loop feed-back process is not employed to optimize the engine running conditions to minimize regulated emissions. Thus, it is quite desirable to employ a closed-loop control process to assure properly controlled engine operation at the leanest condition without the fear of a stall or misfire from operating too lean.
One known prior art approach to starting an internal combustion engine cold is disclosed in U.S. Pat. No. 4,619,237, issued Oct. 28, 1986 to Auslander et al. Here, a predetermined optimum engine speed in rotations per minute (RPM) is initially maintained or gradually reduced until either the vehicle is driven or the mass air flow of the engine reaches a predetermined value, whichever comes first. The engine RPM is then sensed and, if it is greater than the predetermined optimum RPM, the air/fuel ratio is made leaner. The technique of Auslander however results in an imprecise air/fuel control because the air inducted into the engine cannot be optimized for all operating conditions or fuels and this system can only be useful under predetermined conditions. Engine performance cannot be maintained for a variety of barometric operations, parasitic loads, fuels, or degradation of engine conditions. This process is also only useful for cold starts.
To best obtain a net enleanment condition in a cold engine start or generally any other operating situation, a reliable feedback system is required. Most enabling sensors available at this time, such as the Universal Exhaust Gas Oxygen (UEGO) sensor, are significantly expensive, require a significant warm up period of time, and are not completely reliable. Further, these sensors cannot determine the best enleanment possible on any given vehicle, generally because they only monitor the gases in the engine exhaust system. Fuel that is not utilized in the combustion process (also known as "lost" fuel) will incorrectly influence the exhaust sensor. These sensors are not considered robust enough to maintain control accuracy for the life of the vehicle and they are very sensitive to temperatures or chemical poisons.